Photocopying device

ABSTRACT

Photocopying and magnetic recording re enhanced by employing a recording medium, such as a heat-sensitive paper or a magnetic film adjacent to a semiconductor layer. When the semiconductor is exposed to a low level light image, a charge pattern is created in its surface which is retained and which produces a conductivity pattern in the semiconductor layer. The application of radio-frequency power to the semiconductor converts the conductivity pattern to a heat pattern which is recorded as a visible image on the heat-sensitive paper or as data on the magnetic film.

0 United States Patent [151 3,673,594 Kazan [4 1 June 27, 1972 [5 PHOTOCOPYING DEVICE 3,250,636 5/1966 Wilferth ..346/74 MP [72] Inventor: Benjamin Kazan, Briarclifi Manor, N.Y. OTHER PUBLICATIONS Assign: International BMW Mullins C(lrpon' Magnetic Recording Techniques," H. J. Kump et al. IBM Armonk, Tech. 131111., v01. 8, No. 9, 1966, pg. 1,246. 22 F1 d: March 16 1970 Curie Point Writing on Magnetic Films," L. Mayer, J. of I 1 1 e Applied Physics, June 1958, vol. 29, pg. 1,003. [21] Appl. No.: 19,588

Primary Examiner-Samuel S. Matthews Assistant Examiner-Richard L. Moses [52] US. Cl ..346/74 MT, 250/65 T, 346/74 MP, Atmmey Hanifin and Jancin and George Baron 355/3, 355/17 [51] Ill!- Cl 15/12, 603g [58] Field of Search ..250/65 T; 340/173 CR, 173 PP,

340 173 R, 73 p; 34 74 p 74 p 4 ES, 74 Photocopying and magnetic recording re enhanced by em- 35 5 /3, 17 ploying a recording medium, such as a heat-sensitive paper or a magnetic film adjacent to a semiconductor layer. When the [56] References Cited semiconductor is exposed to a low level light image, a charge pattern is created in its surface which is retained and which UNITED STATES PATENTS produces a conductivity pattern in the semiconductor layer.

The application of radio-frequency power to the semiconduc- Owen T tor converts the conductivity pattern to a h pattern is 3 10431685 7/1962 Rosemhal 346/74 MP recorded as a visible image on the heat-sensitive paper or as 3,512,168 5/1970 Bate 346/74 MT data on the magnetic film 3,355,289 11/1967 Hall et a1 ..346/74 P 3,284,196 11/1966 Mazza ..340/173 TP 8 Clalns, 7 Drawing Figures t 2 R F VOLTAGE 32 36 PI-IOTOCOPYING DEVICE It is known that one can employ a layer of photoconductive or photodielectric material in contact with a heat sensitive material in the photocopying field to attain a reproduction of photographs, written matter, and the like. In such prior art devices, light that is incident on a photoconductive or photodielectric layer can cause a change in conductivity or dielectric constant of such layer as a function of the local light intensity impinging thereon. At substantially the same time .that such variations are created in the photoconductive or photodielectric layer, high frequency electrical power is applied to the layer to produce local r.f. heating. The resultant heat pattern is transferred to the heat-sensitive member to produce a copy of the original image.

Such prior art devices did not have any significant electrical storage capabilities so that the generation of the conductivity or dielectric pattern in the light-sensitive layer required almost simultaneous light exposure of the layer with the r.f. heating. Also to produce the required conductivity changes, the radiation from the subject that impinges on the light-sensitive layer had to be relatively intense.

The present invention employs a light-sensitive layer in combination with a recording member to achieve photocopying, but departs from the known state of the art by employing a light-sensitive layer on which a surface charge pattern can be established in response to light emanating from the subject to be copied. This stored charge pattern is retained for long periods after the actuating light is removed. Additionally, such a charge pattern locally controls by field-effect action the conductivity of the underlying semiconductor in a manner similar to that in a thin film field-effect transistor. An r.f. electric field applied to the semiconductor can then cause local current flow in accordance with the surface stored charge pattern. This current flow produces local heating which is directly transferred to the adjacent heat-sensitive layer in which a pattern is recorded corresponding to the optical input image. Since each small or elemental area of the semiconductor can be considered a power amplifier (the optical energy required to produce the surface charge being much less than the r.f. heat developed), the light intensity required for producing a recorded image may be much lower than in prior art photocopy The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention as illustrated in the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIGS. la-le show a series of steps depicting the operation of an embodiment of the invention as it is applied to the recording in a magnetic film.

FIG. 2 is another embodiment of the invention showing recording on a heat-sensitive paper.

FIG. 3 is a further embodiment of the invention wherein the charge storing mechanism consists of a compound layer of an insulator and a semiconductor layer.

In FIG. la is shown an insulating substrate 2, preferably but not limited to glass, ceramic or the like, on which is deposited a thin layer of magnetic material 4. Solely for the purpose of illustrating and not limiting the invention, such film 4 is chosen to be europium oxide (EuO), whose magnetic field direction can be altered by Curie point switching, such EuO being maintained at a temperature below its Curie temperature. In contact with film 4 is a thin semiconductor layer 6 of zinc oxide (ZnO).

As an initial step in the operation of the structure of FIG. 1a for magnetic recording, a magnetic field M (See FIG. lb) is applied thereto so that the entire EuO layer is magnetized in a direction that lies parallel to the plane of the magnetic film, the layer remaining magnetized in that direction after the applied field M has been removed. In FIG. 1c, the surface of the ZnO layer 6 is uniformly charged negatively by a corona generator 8 while the structure is maintained in the dark. To

enable excess negative charges within the ZnO layer 6 to leak ofl', the magnetic film 4 is maintained at ground potential. In FIG. 1d, the ZnO layer 6 is exposed to a transient light image corresponding to subject S.

Such a light pattern locally discharges the ZnO, leaving a charge pattern on the surface of the ZnO. The special characteristics of ZnO which allow it to retain a negative surface charge which can be dissipated by light are discussed in greater detail in an article entitled A Review of Electrofax' Behavior by .I. A. Arnick, RCA REVIEW, December 1969, Vol. XX, No. 4, Pp. 753+. FIG. 1e illustrates the final record ing step wherein successive areas of the magnetic film 4 and ZnO layer 6 are subjected to an r.f. field by moving the composite film 4 and 6 relative to r.f. electrodes 12, at the same time that a magnetic field M, opposite to the aligning field M, is applied to the EuO. In accordance with the charge pattern created by the above-noted procedure, a conductivity pattern produced by field-effect will exist in the ZnO. The generation of a conductivity pattern by a surface charge pattern in ZnO is discussed in an article entitled Image Storage Panels Based on Field-Effect Control of Conductivity by B. Kazan et al, appearing in the PROC. OF-Tl-IE IEEE, 1968, No. 56, Pp. 285-295. The localized heating caused by the r.f. field, where the ZnO is conducting (i.e., discharged), raises the temperature of the EuO above its Curie temperature so that, upon cooling, the heated areas of the EuO are left with a magnetization in the direction of M, eversed from their initial directions of magnetization. Hence, information, in accordance with the stored charge (or optical input), is recorded in the magnetic film 4.

The frequency of the r.f. power applied through electrodes 12 is chosen so that the heat generated is confined mainly to the ZnO. In recording on a magnetic film, it is preferable to use a ZnO material sufficiently doped with excess Zn, for example, so that its conductivity range is sufficiently high. Also, as little r.f. heating as possible should be generated in the magnetic film 4 itself which should have a very low conductivity. In the case of EuO, for example, its bulk resistivity may be as high as 10 ohm-cm. as compared with a resistivity range of 10 -10 ohm-cm. for ZnO so that preferential heating of the ZnO over the EuO is achieved.

For exposing the ZnO 6, the latter may be scanned either with a laser beam or an incoherent intensity-modulated light beam instead of exposing it to an optical image as in the recording process described above. When a laser beam is used, because of its greater spot intensity, it need dwell only a very short time on the successive elemental areas of ZnO layer 6 to generate a charge pattern, permitting faster scanning rates to be achieved than when a beam of incoherent light is used. The highly desirable features of the embodiment of the invention set forth in FIGS. la to 1e are that one obtains a stored latent charge image that can be retained for long periods or erased, and which can be converted to a recorded magnetic pattern at an arbitrary later time. The magnetic pattern, in turn, may be erased merely by applying a sufiiciently uniform field M to the EuO 4 and the recording process repeated.

Although the recording steps have been indicated as distinct sequential steps, it should be clear that the composite layers 2, 4 and 6 could be housed in a light-tight box, such as a camera, and be made to move sequentially past a magnetizing station, a corona charging station, a modulated light station and a radio-frequency station, all such stations being judiciously located at different points of travel of the composite layered unit.

FIG. 2 depicts an embodiment of the invention wherein a heat-sensitive paper 14 is in contact with or coated with a ZnO layer 6 and serves as the recording member. The double-layer film of ZnO and heat-sensitive paper in the form of an elongated movable strip are contained in a camera 16 and by actuation of a shutter (not shown) of the camera 16, so that light 10 from subject 18 focused by means of lens 20 is allowed to reach to a portion of layer 6 below the open shutter. Prior to reaching the region of the shutter (not shown), the ZnO surface is exposed to the corona generator 8 which leaves such surface negatively charged. Grounding of conductive roller r of the camera will permit excess charges from the ZnO to leak off, through slightly conductive paper 14. Exposure of the ZnO to light beam 10 produces a stored charge pattern on the ZnO surface, which produces a corresponding conductivity pattern in the ZnO. Such exposed ZnO sheet arrives at station 22 where it passes near r.f. excited gap electrodes 12 which produces localized heating. Heat-sensitive paper 14 is well known in the art (see for example U.S. Pat. No. 3,368,892, which issued Feb. 13, 1968) and is, for example, of the type that will change from a buff or light color to a blue-black when heated to about 100C. One such paper is also called Thermofax paper in the photocopying field. Since the heat produced in the ZnO by the r.f. field will be produced at the stored charge pattern locations, the pattern will be reproduced in the paper. Since ZnO is transparent, the pattern in the paper 14 is visible through the ZnO layer 6.

In the embodiment shown in FIG. 2, the recorded pattern produced in the heat-sensitive paper 14 is retained, but unlike the magnetic film embodiment, it is not erasable. It is also within the purview of this invention to replace the heat-sensitive layer, if desired, with other heat-sensitive materials such as cholesteric liquid crystals, which change color when heated. Although the images produced in such liquid crystal films are temporary, the use of a field-effect layer 6 for controlling such films provides a type of dynamic display device.

FIG. 3 illustrates an embodiment of the invention where the recording member 4 could be magnetic film, heat-sensitive paper or crystals. Here the ZnO layer is replaced by a thin layer of semiconductor material 34 and insulator 36. The insulator 36 may be, for example, SiO or CaF and the semiconductor may be, for example, CdSe, CdS, or tellurium and is preferably a semiconductor that can be readily fabricated in thin film form. Unlike ZnO, such semiconductors are unable to retain a surface charge without the aid of an insulator coatmg.

By means of an array of stylii 38 (only one of which is shown) close to, or in contact with, the insulating surface 26, the individual voltages, V,, are modulated in accordance with input signals as the composite film is moved past the stylii 38. In this manner, a charge pattern can be established on the insulating surface 36. Assuming that the composite layers comprising recording member 32, semiconductor 34 and insulator 36 move in the direction of the arrow, maintaining an r.f. voltage across electrodes 12 causes localized heating to take place within semiconductor 34, such heating taking place in accordance with the conductivity produced in the semiconductor by the stored charge pattern. This localized heating is then transferred to the heat-sensitive recording member 32, which can form either a permanent or erasable record. In the embodiment of FIG. 3, it is assumed that recording member 32 is slightly conducting and maintained at ground potential, by means of roller r which is grounded, to enable excess negative charges to leak off the film 32 during corona charging. Grounded roller r also transports the composite film.

What is claimed is:

l. A photocopying device comprising a heat-sensitive recording element,

a field-effect controlled semiconductor contacting said element, means for establishing a charge pattern in the form of electrical conductivity variations on the surface of said semiconductor, and

radio-frequency electric field means for locally heating said semiconductor so as to reproduce said stored charge pattern as a visible image on said recording element.

2. A photocopying device comprising a heat-sensitive recording element,

a field-efiect controlled semiconductor layer in contact with said recording element, means for exposing said semiconductor to an optical image so as to store a charge pattern in said semiconductor in accordance with the intensity of light emanating from said image, and

means for applying a radio-frequency electric field to said semiconductor so as to locally heat said semiconductor and reproduce said stored charge pattern as a visible image onto said recording element.

3. The photocopying device of claim 2 wherein said field-effect controlled semiconductor is ZnO.

4. A photocopying device comprising a heat-sensitive recording element,

a field-effect controlled composite layer comprising a semiconductor and an electrical insulator adjacent said heat-sensitive recording element,

means for establishing a charge pattern on said insulating surface by a direct flow of charge to said insulating surface, and

means for applying a radio-frequency field to said semiconductor so as to locally heat said semiconductor and reproduce said stored charge pattern as a visible image on said recording element.

5. In a method of photocopying an image comprising the steps of providing a field-effect controlled semiconductor in contact with a heat-sensitive recording element,

applying a uniform negative charge to said semiconductor while maintaining the latter in the dark,

exposing said uniformly charged semiconductor to said image so as to produce a stored charge pattern in said semiconductor in accordance with the intensity of the light emanating from said image, and

applying a radio-frequency electric field to said semiconductor so as to locally heat said semiconductor and reproduce said stored charge pattern as a visible image onto said recording element.

6. In a method of photocopying data comprising the steps of providing a field-effect controlled semiconductor in contact with a heat-sensitive recording element,

applying an electric field to the surface of said semiconductor, said electric field being modulated by said data to be copied so as to provide a stored charge pattern on said semiconductor, and

applying a radio-frequency electric field to locally heat said semiconductor and thus reproduce said stored charge pattern onto said heat-sensitive recording element. 7. In a method of photocopying data onto a magnetic recording element comprising the steps of providing a field-effect controlled semiconductor in contact with a heat-sensitive magnetic film maintained below its Curie point,

uniformly magnetizing said film in a first direction, uniformly charging said semiconductor with a negative charge while maintaining said semiconductor in the dark,

exposing said field-effect controlled semiconductor to light emanating from said data so as to provide a stored charge pattern on said semiconductor, and

applying r.f. power to said semiconductor at the same time that a second magnetic field, opposite to said first direction, is applied to said magnetic film whereby the heat generated by said r.f. power in accordance with charge pattern raises the temperature of the magnetic film above its Curie point so that a magnetic image of said data is stored in said magnetic recording element.

8. In a method of claim 7 wherein said magnetic recording element is EuO. 

1. A photocopying device comprising a heat-sensitive recording element, a field-effect controlled semiconductor contacting said element, means for establishing a charge pattern in the form of electrical conductivity variations on the surface of said semiconductor, and radio-frequency electric field means for locally heating said semiconductor so as to reproduce said stored charge pattern as a visible image on said recording element.
 2. A photocopying device comprising a heat-sensitive recording element, a field-effect controlled semiconductor layer in contact with said recording element, means for exposing said semiconductor to an optical image so as to store a charge pattern in said semiconductor in accordance with the intensity of light emanating from said image, and means for applying a radio-frequency electric field to said semiconductor so as to locally heat said semiconductor and reproduce said stored charge pattern as a visible image onto said recording element.
 3. The photocopying device of claim 2 wherein said field-effect controlled semiconductor is ZnO.
 4. A photocopying device comprising a heat-sensitive recording element, a field-effect controlled composite layer comprising a semiconductor and an electrical insulator adjacent said heat-sensitive recording element, means for establishing a charge pattern on said insulating surface by a direct flow of charge to said insulating surface, and means for applying a radio-frequency field to said semiconductor so as to locally heat said semiconductor and reproduce said stored charge pattern as a visible image on said recording element.
 5. In a method of photocopying an image comprising the steps of providing a field-effect controlled semiconductor in contact with a heat-sensitive recording element, applying a uniform negative charge to said semiconductor while maintaining the latter in the dark, exposing said uniformly charged semiconductor to said image so as to produce a stored charge pattern in said semiconductor in accordance with the intensity of the light emanating from said image, and applying a radio-frequency electric field to said semiconductor so as to locally heat said semiconductor and reproduce said stored charGe pattern as a visible image onto said recording element.
 6. In a method of photocopying data comprising the steps of providing a field-effect controlled semiconductor in contact with a heat-sensitive recording element, applying an electric field to the surface of said semiconductor, said electric field being modulated by said data to be copied so as to provide a stored charge pattern on said semiconductor, and applying a radio-frequency electric field to locally heat said semiconductor and thus reproduce said stored charge pattern onto said heat-sensitive recording element.
 7. In a method of photocopying data onto a magnetic recording element comprising the steps of providing a field-effect controlled semiconductor in contact with a heat-sensitive magnetic film maintained below its Curie point, uniformly magnetizing said film in a first direction, uniformly charging said semiconductor with a negative charge while maintaining said semiconductor in the dark, exposing said field-effect controlled semiconductor to light emanating from said data so as to provide a stored charge pattern on said semiconductor, and applying r.f. power to said semiconductor at the same time that a second magnetic field, opposite to said first direction, is applied to said magnetic film whereby the heat generated by said r.f. power in accordance with charge pattern raises the temperature of the magnetic film above its Curie point so that a magnetic image of said data is stored in said magnetic recording element.
 8. In a method of claim 7 wherein said magnetic recording element is EuO. 